I had a good experience with a Radeon 9250 (it's a crappy card, but it's enough for very old games) and then i had Radeon 1650 Pro which is an ok card in the "bang for your buck" cathegory. Both are from Ati and the 1650 requires a minimum 400W PSU.
i found something does geforce 7600 better than a geforce 6800? i found it here http://www.inno3d.com/products/graphic_card/gf7_agp/7600gs.htm
I looked around online, and it seems most sellers don't sell the 7600 anymore. http://www.newegg.com/Product/Product.aspx?Item=N82E16814133176 http://www.amazon.com/PNY-Geforce-7600GS-512MB-Agp/dp/B000H70X3A/ref=sr_1_5?ie=UTF8&s=electronics&qid=1238252877&sr=1-5
a 7600 may not be better than a 6800. The 7600 is a mid range 7 series card, whereas the 6800 is a high end 6 series.
no, it's a newer series, and the ends always overlap. A high end card in one series is always better than the entry level card in the next series.